Magnetorheological fluids are magnetic field responsive fluids containing a field polarizable particle component and a liquid carrier component. Magnetorheological fluids are useful in devices or systems for controlling vibration and/or noise. Magnetorheological fluids have been proposed for controlling damping in various devices, such as dampers, shock absorbers, and elastomeric mounts. They have also been proposed for use in controlling pressure and/or torque in brakes, clutches, and valves. Magnetorheological fluids are considered superior to electrorheological fluids in many applications because they exhibit higher yield strengths and can create greater damping forces.
The particle component compositions typically include micron-sized magnetic-responsive particles. In the presence of a magnetic field, the magnetic-responsive particles become polarized and are thereby organized into chains of particles or particle fibrils. The particle chains increase the apparent viscosity (flow resistance) of the fluid, resulting in the development of a solid mass having a yield stress that must be exceeded to induce onset of flow of the magnetorheological fluid. The particles return to an unorganized state when the magnetic field is removed, which lowers the viscosity of the fluid.
Magnetorheological (MR) fluids based on hydrocarbon or silicone oils are well-known in the literature and numerous patents, and many device applications based on these fluids are also known. Aqueous magnetorheological fluids are also known, but there are fewer device applications for this fluid because of its limited temperature stability and its lack of lubricity. Hydrocarbon-based magnetorheological fluids have been found to be unsatisfactory in devices that contain natural rubber (e.g., automotive engine mounts) due to an incompatibility between the rubber and the hydrocarbon carrier fluid. Silicone-based fluids are more compatible with the rubber material, but they are generally more expensive and are not as desirable from a user's viewpoint because of the potential for silicone cross-contamination.
Glycol-based fluids are compatible with natural rubber and have acceptable temperature stability without the drawbacks associated with silicone fluids. A patent for glycol-based magnetorheological fluid assigned to Delphi Corporation (U.S. Pat. No. 6,824,700 B2, Glycol-Based MR Fluids with Thickening Agent) uses organoclay as a thickening agent. Such fluids suffer from the drawback that they form a persistent foam when exposed to vacuum, which is a significant problem for vacuum-filling operations typically used by engine mount manufacturers.
The purpose of this invention is to provide a glycol-based fluid with minimal settling that is non-foaming and satisfactory for use in engine mounts or similar devices.